How To Fix Pixelated Cycles 3D Viewport Editor
To echo @brockmann (who commented), eight samples is very, very, very low. If your graphics card is working with cycles render, I would at least use 512 samples and work from there.
Edit: I was unable to find questions on what samples are, so I guess I’ll explain it myself. A “sample” is one shot of data for rendering, and more shots mean better looking renders, just like more signal flares with more wind conditions will give you a better idea of where the ship is. In Cycles, a sample is a single ray of light, traced backwards out of a camera, through a pixel, hitting what it may until it gets to a light source, thus defining what color that pixel of the image should be. An “importance map” is made just before the rest of the rendering which maps out where lights are in the scene, so the backwards-traced rays will be more likely to go towards them and not oblivion. The blender manual at docs.blender.org explains it better, but basically, a light ray will bounce in an arbitrary direction if it hits a rough surface, and a more predictable direction if it hits a smooth one. Few samples will then return a lot of fuzz on rough objects. “Caustics” is another place where fuzz can be created, where light being bounced around by mirrors or glass can have a hard time finding a light source from the “importance map.” Thus, there is a lot of fuzz in your cube as only eight rays work on each pixel: it’s like calling eight random people in a country to find out how popular a TV show is. One set of eight might indicate no popularity, while another is more correct, while still another indicates that everyone watches that TV show. Lots of samples means lots of rays, lots of tested directions light could be coming from, and lots more actual representation of what kind of light is hitting that spot. More samples also means more computing time, but if you’ve got time for how long your computer (or GPU) takes, go ahead and do it.
NVidia is the best, so you can probably do a lot of samples